1. Field of the Invention
The present invention relates generally to apparatus and methods for maintaining patency in body passages and, more particularly, to the construction and use of an intraluminal stent having the ability to periodically disrupt invasive tissue growth.
The occlusion of body passages is frequently a side effect of solid tumor growth. Such occlusion is often life threatening and almost always a cause of great discomfort to the patient. The most common method for re-opening body passages which have been blocked by tumor growth has been surgical intervention where the occluding material is excised.
Surgical intervention, however, is undesirable due to the risk of post-operative complications.
Furthermore, the beneficial effect of such surgical intervention is frequently short-lived as regrowth of the tumor results in reocclusion of the body passage. Thus, it would be desirable to provide apparatus and methods which do not require major surgical intervention and which are able to maintain patency in the body passage for a longer period of time, preferably indefinitely.
The use of intraluminal stents to maintain patency in body passages subject to occlusion by invasive tumor growth has been proposed. See, for example, U.S. Pat. Nos. 4,699,611 and 4,580,658. The use of such stents, however, is problematic in several respects. The use of perforate stents, such as the mesh stents described in U.S. Pat. No. 4,580,658, frequently allows invasive tissue growth through the interstices in the wall of the stent. Thus, although the stent may inhibit the invasive growth for a time, reocclusion frequently occurs. Moreover, the presence of the stent enmeshed in the subsequent tumor growth can inhibit recanalization of the passage.
The tendency of perforate stents to allow reocclusion of the body passage can be overcome by the use of solid-wall stents, as described in U.S. Pat. No. 4,699,611. A solid wall can physically block the intrusion of the tumor cells into the lumen defined therein. Such solid-wall stents, however, also suffer from disadvantages. It is difficult to construct solid-wall stents which are expandable, so it is usually necessary to insert the stent in its full-sized configuration. (This is not true of mesh and other perforate stents which may be expanded to their final dimensions after being located within the body passage.) Solid-wall stents can also inhibit the supply of nutrients to and elimination of wastes from the tissue surrounding the body passage. Such blockage cannot only interfere with necessary bodily functions, but can also cause tissue necrosis which is undesirable in many circumstances. Finally, solid-wall stents are themselves subject to reocclusion as they tend to promote axial spreading of the tumor, which can block the lumen through the stent at either or both ends.
For these reasons, it would be desirable to provide improved apparatus and methods for maintaining patency within body passages subject to tumor growth. It would be particularly desirable if such apparatus and methods could inhibit reocclusion of the body passage without substantially inhibiting the normal exchange of nutrients and waste between said passage and the surrounding tissue. It would be further desirable if the apparatus and methods could be adapted to most or all body passages, including the urinary tract, the biliary tract, respiratory passages, pancreatic ducts, lymphatic ducts, and the like. The apparatus should be easy to implant (not requiring major surgery for implantation), and use of the apparatus should not result in release of viable tumor cells from the primary site being treated.
2. Description of the Background Art
The construction and use of stents which may be used to maintain patency in body passages subject to invasive tumor growth are described in U.S. Pat. Nos. 4,699,611; 4,580,568; and 4,800,882. U.S. Pat. Nos. 4,795,458 and 4,665,906, each disclose the use of heat to expand a stent within the body passage, usually a blood vessel. The stents are generally heated by an external source and do not possess or provide sufficient thermal energy to disrupt surrounding tissue growth. Other stent structures are disclosed in U.S. Pat. Nos. 4,830,003; 4,795,465; 4,705,516; 4,680,031; 4,655,771; 4,202,331; 4,035,849; and 3,983,581. Electrosurgery techniques employing bipolar radio frequency generators to deliver energy to electrodes for making surgical incisions are known.